Efforts have been made to determine the etiological agent in multiple sclerosis. Several new techniques to determine humoral and cellular immune responses have been made. These include direct migration inhibition, lymphocyte cytoxicity and comediated antibody cytotoxicity studies. Mice have been inoculated with human MS and control brain material in an effort to confirm the association of the mouse PMN depressing agent and multiple sclerosis. A highly specific antibody against Simian Hemorrhagic fever virus has been produced in guinea pigs. Identification of chronic carriers using the complement fixation test were not very successful.